feat(web): add i18n locale routes and language switcher component

Add locale-prefixed routes for admin, auth, dashboard, and public pages.
Add error, loading, and not-found pages for locale context. Add language
switcher UI component for Vietnamese/English toggle.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/app/[locale]/auth/callback/google/page.tsx

@@ -0,0 +1,55 @@
+'use client';
+
+import { Loader2 } from 'lucide-react';
+import { useRouter, useSearchParams } from 'next/navigation';
+import { useEffect, useRef } from 'react';
+import { useAuthStore } from '@/lib/auth-store';
+
+export default function GoogleCallbackPage() {
+  const router = useRouter();
+  const searchParams = useSearchParams();
+  const { handleOAuthCallback } = useAuthStore();
+  const processed = useRef(false);
+
+  useEffect(() => {
+    if (processed.current) return;
+    processed.current = true;
+
+    const accessToken = searchParams.get('accessToken');
+    const refreshToken = searchParams.get('refreshToken');
+    const expiresIn = searchParams.get('expiresIn');
+    const error = searchParams.get('error');
+
+    if (error) {
+      router.replace(`/login?error=${encodeURIComponent(error)}`);
+      return;
+    }
+
+    if (!accessToken || !refreshToken) {
+      router.replace('/login?error=oauth_failed');
+      return;
+    }
+
+    handleOAuthCallback(
+      accessToken,
+      refreshToken,
+      expiresIn ? Number(expiresIn) : 900,
+    )
+      .then(() => {
+        const redirect = searchParams.get('redirect') || '/dashboard';
+        router.replace(redirect);
+      })
+      .catch(() => {
+        router.replace('/login?error=oauth_failed');
+      });
+  }, [searchParams, handleOAuthCallback, router]);
+
+  return (
+    <div className="flex min-h-screen items-center justify-center">
+      <div className="text-center">
+        <Loader2 className="mx-auto h-8 w-8 animate-spin text-primary" />
+        <p className="mt-4 text-sm text-muted-foreground">Đang xử lý đăng nhập Google...</p>
+      </div>
+    </div>
+  );
+}

apps/web/app/[locale]/auth/callback/zalo/page.tsx

@@ -0,0 +1,55 @@
+'use client';
+
+import { Loader2 } from 'lucide-react';
+import { useRouter, useSearchParams } from 'next/navigation';
+import { useEffect, useRef } from 'react';
+import { useAuthStore } from '@/lib/auth-store';
+
+export default function ZaloCallbackPage() {
+  const router = useRouter();
+  const searchParams = useSearchParams();
+  const { handleOAuthCallback } = useAuthStore();
+  const processed = useRef(false);
+
+  useEffect(() => {
+    if (processed.current) return;
+    processed.current = true;
+
+    const accessToken = searchParams.get('accessToken');
+    const refreshToken = searchParams.get('refreshToken');
+    const expiresIn = searchParams.get('expiresIn');
+    const error = searchParams.get('error');
+
+    if (error) {
+      router.replace(`/login?error=${encodeURIComponent(error)}`);
+      return;
+    }
+
+    if (!accessToken || !refreshToken) {
+      router.replace('/login?error=oauth_failed');
+      return;
+    }
+
+    handleOAuthCallback(
+      accessToken,
+      refreshToken,
+      expiresIn ? Number(expiresIn) : 900,
+    )
+      .then(() => {
+        const redirect = searchParams.get('redirect') || '/dashboard';
+        router.replace(redirect);
+      })
+      .catch(() => {
+        router.replace('/login?error=oauth_failed');
+      });
+  }, [searchParams, handleOAuthCallback, router]);
+
+  return (
+    <div className="flex min-h-screen items-center justify-center">
+      <div className="text-center">
+        <Loader2 className="mx-auto h-8 w-8 animate-spin text-primary" />
+        <p className="mt-4 text-sm text-muted-foreground">Đang xử lý đăng nhập Zalo...</p>
+      </div>
+    </div>
+  );
+}